In the submarine technical sector it is known that, when the submarine is at periscope depth, a predetermined number of passive and active sensors have to be carried out of the water, for example radar and/or radio antennae, optronic heads and the like, which are normally housed in the submarine conning tower (or sail). When necessary, these submarine-atmospheric interface devices are translated vertically by suitable lifting apparatuses, until the sensors emerge from the surface of the water above the conning tower.
It is also known that these lifting apparatuses are required to be particularly silent, to avoid being detected by acoustic sensors; resistant to underwater pressure at the depths which the submarine navigates at; resistant to corrosion by seawater; and capable of lifting the sensor lifting apparatus or mast on the mast guides, overcoming not only its own weight but also the friction generated by the hydrodynamic thrust of the water caused by submarine motion, a transversal thrust which produces most of the overall resistance to the translational movement in the vertical direction.
Other technical specifications required of the lifting apparatuses are low magnetic signature and reduced size allowing them to fit into extremely small spaces.
Some of the above requirements are met by apparatuses with oil-hydraulic drives which, however, require a hydraulic system comprising, amongst other things, a pumping station, involving constructional complications and higher maintenance requirements to protect hydraulic fluid from water infiltrations.
Traditional hydraulic drives were improved by the introduction of electric drives, which allow precision control, low maintenance and less structural complexity.
Document EP1847454, in the name of the same Applicant as this invention, describes solutions with traditional rotary electric motors which, however, need complex and noisy mechanisms which must fit into the lifting apparatus in order to protect the motor from the water and high underwater pressure. As a result, there is no significant reduction either in acoustic signature or hydrodynamic resistance.
As described in document EP1739006, in the name of the same Applicant as this invention, it is also possible to use linear electric motors, which, however, have potential properties of low density and energy efficiency and which require high electric currents and volumes.
Other solutions involve using linear motors with permanent magnets which have the disadvantage of being characterized by extended windings on the guide or by magnets mounted on the selfsame guide which expose the submarine to a magnetic signature making it easier to detect.
Furthermore, in the past other solution have been disclosed, all relating to the use of a belt (or chain) member, or similar deformable means, in a transmission system.
Some of those solutions are published, for example, in patent documents U.S. Pat. No. 1,290,745, U.S. Pat. No. 1,298,333, GB146433 and NL10072.
However, such documents only disclose a simple belt transmission having a couple of pulleys, a driving one and a driven one.